Re: Compressed Filesystem

Roland
2008-12-16T19:45:13Z

>I agree that adding more options will add more complexity but it seems
> the same amount of work in kernel space will have to be done

regarding lzo compression itself - it`s already there(since july 2007).
the in-kernel lzo is equivalent to minilzo.
(http://www.oberhumer.com/opensource/lzo/)

regards
roland

----- Original Message -----
From: "Lee Trager" <lt73@cs.drexel.edu>
To: "Chris Mason" <chris.mason@oracle.com>
Cc: "Lee Trager" <lt73@cs.drexel.edu>; <devzero@web.de>;
<linux-btrfs@vger.kernel.org>
Sent: Tuesday, December 16, 2008 5:25 PM
Subject: Re: Compressed Filesystem

>I agree that adding more options will add more complexity but it seems
> the same amount of work in kernel space will have to be done. If we
> support mutiple compression schemes somewhere the compression scheme
> used will have to be stored so we know what to use in the future. If we
> store it on the super block the user will have to choose when they
> format at which point they may not see the need to use compression. Or
> they may choose one compression scheme and later want to change to
> something else. It doesn't make sence to have to reformat your drive
> just to change compression scheme. This leaves us with storing what the
> compression scheme is on each inode. We currently store if compression
> is used on a per inode basis so storing the type wouldn't be a huge
> leap.
>
> Lee
> On Tue, Dec 16, 2008 at 10:26:10AM -0500, Chris Mason wrote:
>> On Tue, 2008-12-16 at 10:20 -0500, Lee Trager wrote:
>> > While I agree that the command you send should be possible it wasn't
>> > exactly what I was thinking. Currently I am working on a way for the
>> > user to individually set which files/directories they want compressed
>> > or
>> > not. What I was saying is that assuming you are in a mounted btrfs
>> > directory you could do something like
>> >
>> > chattr -R +c zlib dir1 Compress dir1 and all its contents with zlib
>> > chattr -R +c bzip dir2 Compress dir2 and all its contents with bzip
>> > chattr +c lzo file1 Compress fil1 with lzo
>> > chattr -c file2 Uncompress file2
>> > chattr +c none dir3 Uncompress dir3 but leave contents as is
>> >
>> > If the user did something like
>> > mount -o compress,cscheme=zlib /dev/xyz /mntpoint
>> > and then
>> > chattr +c /mntpoint/dir
>> > /mntpoint/dir would default to zlib as would anything else written to
>> > the disk.
>> >
>>
>> This is one of those places where more options isn't always better.
>> Every option adds complexity to the filesystem and the testing matrix.
>>
>> I'd much rather have just one compression scheme per FS. If people need
>> a specific compression scheme for a specific file, they can just
>> compress it in userland.
>>
>> -chris
>>
>>
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